1. Technical Field
This disclosure relates to voltage reference circuits, including bandgap voltage reference circuits, in which changes in the ratio between the emitter areas of two transistors in the circuit may adversely affect the stability of the reference voltage.
2. Description of Related Art
A voltage reference circuit may provide a substantially constant output voltage, notwithstanding changes in input voltage, temperature, and/or other conditions.
The stability of the output voltage may depend upon the stability of the ratio between the emitter areas of two transistors, one of which may have a substantially larger emitter area than the other. That ratio, however, may be affected by thermal hysteresis—mechanical stresses imposed unequally by temperature changes on different portions of the transistors. This may be particularly true when the voltage reference circuit is contained on a single die.
Efforts have been made to compensate for the adverse effects of thermal hysteresis. For example, the transistor with the smaller emitter area has been centered within a group of individual transistors that collectively function as the transistor with the larger emitter area. However, this approach may not solve the problem for certain types of stresses.